1. Technical Field
The present invention relates to endoluminal vascular prostheses and methods of deploying such prostheses, and, in one application, to endoluminal vascular prostheses for use in the treatment of vessels with branches.
2. Description of the Related Art
An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta, a major artery of the body, as it passes through the abdomen. The abdomen is that portion of the body that lies between the thorax and the pelvis. It contains a cavity, known as the abdominal cavity, separated by the diaphragm from the thoracic cavity and lined with a serous membrane, the peritoneum. The aorta is the main trunk, or artery, from which the systemic arterial system proceeds. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries.
The aneurysm usually arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. When left untreated, the aneurysm may eventually cause rupture of the sac with ensuing fatal hemorrhaging in a very short time. High mortality associated with the rupture led initially to transabdominal surgical repair of abdominal aortic aneurysms. Surgery involving the abdominal wall, however, is a major undertaking with associated high risks. There is considerable mortality and morbidity associated with this magnitude of surgical intervention, which in essence involves replacing the diseased and aneurysmal segment of blood vessel with a prosthetic device which typically is a synthetic tube, or graft, usually fabricated of polyester, urethane, Dacron®, Teflon®, or other suitable material.
To perform the surgical procedure requires exposure of the aorta through an abdominal incision which can extend from the rib cage to the pubis. The aorta must typically be closed both above and below the aneurysm, so that the aneurysm can then be opened and the thrombus, or blood clot, and arteriosclerotic debris removed. Small arterial branches from the back wall of the aorta are tied off. The Dacron® tube, or graft, of approximately the same size of the normal aorta is sutured in place, thereby replacing the aneurysm. Blood flow is then reestablished through the graft. It is necessary to move the intestines in order to get to the back wall of the abdomen prior to clamping off the aorta.
If the surgery is performed prior to rupturing of the abdominal aortic aneurysm, the survival rate of treated patients is markedly higher than if the surgery is performed after the aneurysm ruptures, although the mortality rate is still quite high. If the surgery is performed prior to the aneurysm rupturing, the mortality rate is typically slightly less than 10%. Conventional surgery performed after the rupture of the aneurysm is significantly higher, one study reporting a mortality rate of 66.5%. Although abdominal aortic aneurysms can be detected from routine examinations, the patient does not experience any pain from the condition. Thus, if the patient is not receiving routine examinations, it is possible that the aneurysm will progress to the rupture stage, wherein the mortality rates are significantly higher.
Disadvantages associated with the conventional, prior art surgery, in addition to the high mortality rate include the extended recovery period associated with such surgery; difficulties in suturing the graft, or tube, to the aorta; the loss of the existing aorta wall and thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients having abdominal aortic aneurysms; and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. A patient can expect to spend from one to two weeks in the hospital after the surgery, a major portion of which is spent in the intensive care unit, and a convalescence period at home from two to three months, particularly if the patient has other illnesses such as heart, lung, liver, and/or kidney disease, in which case the hospital stay is also lengthened. Since the graft must typically be secured, or sutured, to the remaining portion of the aorta, it is many times difficult to perform the suturing step because the thrombosis present on the remaining portion of the aorta, and that remaining portion of the aorta wall may be friable, or easily crumbled.
Since many patients having abdominal aortic aneurysms have other chronic illnesses, such as heart, lung, liver, and/or kidney disease, coupled with the fact that many of these patients are older, the average age being approximately 67 years old, these patients are not ideal candidates for such major surgery.
More recently, a significantly less invasive clinical approach to aneurysm repair, known as endovascular grafting, has been developed. Parodi, et al. provide one of the first clinical descriptions of this therapy. Parodi, J. C., et al., “Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,” 5 Annals of Vascular Surgery 491 (1991). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft in the endoluminal position (within the lumen of the artery). By this method, the graft is attached to the internal surface of an arterial wall by means of attachment devices (expandable stents), typically one above the aneurysm and a second stent below the aneurysm.
Stents can permit fixation of a graft to the internal surface of an arterial wall without sewing or an open surgical procedure. Expansion of radially expandable stents is conventionally accomplished by dilating a balloon at the distal end of a balloon catheter. In U.S. Pat. No. 4,776,337, for example, Palmaz describes a balloon-expandable stent for endovascular treatments. Also known are self-expanding stents, such as described in U.S. Pat. No. 4,655,771 to Wallsten.
In certain conditions, the diseased region of the blood vessels can extend across branch vessels. The blood flow into these branch vessels is critical for the perfusion of the peripheral regions of the body and vital organs. Many arteries branch off the aorta. For example, the carotid arteries supply blood into the brain, the renal arteries supply blood into the kidneys, the superior mesenteric artery (“SMA”) supplies the pancreas, the hypogastric arteries supply blood to the reproductive organs, and the subclavian arteries supply blood to the anus. When the aorta is diseased, the branch vessels may also be affected. Thoracic aortic aneurysms may involve the subclavian and carotid arteries, abdominal aneurysms may involve the SMA, renal and hypogastric arteries. Aortic dissections may involve all branch vessels mentioned above. When this occurs, it may be detrimental to implant a conventional tubular graft in this location of the aorta or the blood vessel, since such a graft may obstruct the flow of blood from the aorta into the branches.
Grafts and graft systems are typically used to treat aneurysms in the aorta or in other blood vessels. These grafts can be positioned within the aorta or other blood vessels at the location of an aneurysm and, generally speaking, can provide a synthetic vessel wall that channels the flow of blood through the diseased portion of the blood vessel. As such, the grafts are typically fluid impermeable so that no blood can flow through the walls of the graft. Rather, the blood is channeled through the central passageway defined by the graft.
Thus, there is a need to place endoluminal prostheses in the aorta without obstructing critical branch vessels. The embodiments of the endoluminal prostheses disclosed herein provide a solution to the problems described above.